Tertiary industry has developed rapidly and became a significant pillar of economic growth. Simultaneously, service quality is gradually becoming an importance factor which restricts its development. The employees who are the main carriers of service values need to interact with customers frequently. Against this background, how to enhance employees’ organizational citizenship behavior（OCB) to meet customer requirements and improve the service quality have drawn increasing attentions from research and practice communities. However, the previous studies are mainly from a single perspective, more efforts are needed to investigate the relationship between person-organization fit and OCB from the interactive perspective, which has no consistent conclusion for now. According to the social exchange theory, employee can increase work engagement when they obtain great resources through person-organization fit. Furthermore, person-organization fit includes individual factor and situational factor, which can affect individual behavior based on person-situation interactionist theory. Individual factor and situational factor may also effect the relationship between person-organization fit and OCB, to strengthen or weaken the relationship. Therefore, this current study discusses the effect of person-organization fit on OCB. Specially, this paper introduces employee engagement as a mediator, proactive personality and supervisor support as the moderators which represent individual factor and situational factor respectively. Moreover, we proposed a moderated mediation model to disentangle the underlying mechanism and boundary condition of the relationship between person-organization fit and OCB. We adopted questionnaire research method to test our proposed hypotheses. Initially, we issued 270 questionnaires, and finally used a sample of 225 employees from 12 restaurants. Consistent with our hypotheses, the results indicated that: （1)person-organization fit positively predicts organizational citizenship behavior, with the effect mediated by employee engagement; （2)supervisor support moderates the mediation effect between person-organization fit and organizational citizenship behavior, indicating that the indirect effect became stronger among those who receive higher leader support;（3)proactive personality moderates the mediation effect between person-organization fit and organizational citizenship behavior, indicating that the indirect effect became weaker among those who are more proactive. In general, the current study has answered:（1) How does person-organization fit influence employees OCB? （2) Under what condition is person-organization fit more likely to influence OCB? The findings of the current study have substantial theoretical implications as well as practical implications. Theoretically, this paper verifies the positive effect of person-organization fit on OCB. Furthermore, based on social exchange theory, the study advances our knowledge by proposing employee engagement as a mediator. Finally, integrating the individual and organizational factors to the research model according to person-situation interactionist theory, this paper contributes the person-organization fit and OCB literature by raising proactive personality and supervisor support as the moderators. Practically, our research bears implications for tertiary industry as to how to elicit employee organizational citizenship behavior, which include selecting the employees who match with organization, providing enough support and concern to employees, and expecially paying more attention to the employees with high proactive personality as their dynamic demands needed to be satisfied in time. Limitations and future researches are also discussed.